We can solve this together! We're beginning with 39131 and removing 33121 from it.

Step 1: We'll start by subtracting the digit 1 and the borrow 0 from 1 in column 1 and get 0.
0 is the first digit of our result.

Step 2: We'll start by subtracting the digit 2 and the borrow 0 from 3 in column 2 and get 1.
1 is the next digit of our result.

Step 3: We'll start by subtracting the digit 1 and the borrow 0 from 1 in column 3 and get 0.
0 is the next digit of our result.

Step 4: We'll start by subtracting the digit 3 and the borrow 0 from 9 in column 4 and get 6.
6 is the next digit of our result.

Step 5: We'll start by subtracting the digit 3 and the borrow 0 from 3 in column 5 and get 0.
0 is the next digit of our result.

So, 39131 - 33121 = 6010.